Ошибка при работе с шейдером Both a vertex shader and pixel shader must be set on the device before any draw operations may be performed

sampler2D g_samSrcColor;
 
float timeraslow=1.0;
 
float4 MyShader( float2 Tex : TEXCOORD0 ) : COLOR0
{
    float4 Color;
    Tex.y = Tex.y + (sin(timeraslow)*0.01);
    Tex.x = Tex.x + (cos(timeraslow)*0.01);
    Color = tex2D( g_samSrcColor, Tex.xy);
    return Color;
}
 
 
technique PostProcess
{
    pass p1
    {
        VertexShader = null;
        PixelShader = compile ps_2_0 MyShader();
    }
 
}